1. Field of the Invention
The present invention relates to a detection switch circuit for generating an output signal in accordance with the detection result of a detector such as a photo-electric switch a proximity switch or the like, and more particularly to a detection switch circuit the main circuit parts of which are formed integrally on an integrated circuit (IC) substrate.
2. Description of the Related Art
Conventionally, a small-sized detection switch has been integrated as dense as possible to be incorporated in a smaller number of smaller-sized IC substrate(s). One example of typical detection switches formed on the IC substrate will be explained with reference to FIG. 1.
In FIG. 1, a detection switch 1 serves to drive a load device 2 connected therewith in accordance with a detection result, and comprises an IC substrate 3, a detector 4, a display lamp 5 and a delay circuit 6.
The load device 2 may be selected from various kinds of manupulators or displays including a valve solenoid, a magnetic relay, a lamp and a motor in accordance with a control purpose.
The detector 4 which generates a detecting signal based on a detected object or state may be incorporated in the detection switch circuit 1. Also, in accordance with the object to be detected, the detector 4 may be a primary switch such as a limit switch, a magnetic detector, a photo-detector comprising a projector and a receiver and a vibration sensor, or may be a composite sensor such as a moisture sensor, a smoke sensor and an acceleration sensor.
The IC substrate 3 which is the main circuit part of the detection switch 1 comprises a detecting circuit unit 7, an output circuit unit 8 and a power supply circuit 9 formed on a sheet of IC substrate. The IC substrate 3 is also incorporated in the detection switch.
The detecting circuit unit 7 serves to generate a judgment signal relative to the detection object in response to a detection output, and comprises an amplifying circuit 11 and an integrating circuit 12. The amplifying circuit 11 generates a stable output in response to a faint detection output from the detector 4. The integrating circuit 12 processes the stable signal to generate a judgment signal indicative of the judgment result of e.g. the presence of the detection object, the status thereof. If the detecting circuit unit 7 is simple, the above functions may not be separated.
The output circuit unit 8 is provided for insufficiency of the current capacitance of the output from the integrating circuit 12. In response to the judgment signal from the integrating circuit 12, the output circuit unit 8 produces a driving signal for the load device 2 and a display signal for the display lamp 5. The output circuit unit 8 is composed of an output signal generating circuit 13, an output driver 14 and a display circuit 15.
The output signal generating circuit 13 produces an output signal for controlling the load device 2 in accordance with the judgment signal from the integrating circuit 12. In response to the output signal from the circuit 13, the output driver 14 produces a driving signal having a large current capacitance for driving the load device 2. The output driver 14 is designed to have a function of short-circuit protection.
The output driver 14, which is incorporated in the IC substrate, includes an NPN output type and/or a PNP output type. The NPN output type driver comprises an NPN power transistor incorporated on the IC substrate, the output of which is supplied to an external terminal to be directly connected with the load device 2. On the other hand, the PNP output type driver usually comprises an NPN transistor incorporated on the IC substrate and an additional PNP power transistor provided externally. The reason is that the NPN power transistor can be easily designed with a relatively small size and large capacitance, and also the demand therefor is great. On the other hand, the PNP power transistor will be too large considering its current capacitance and also the demand therefor is relatively low. Therefore, it is preferable to externally attach it in accordance with capacity requirement rather than to prepare a large size IC substrate for a low demand. This applies to the detection switch in which both drivers of NPN output type and PNP output type are integrally incorporated on the same IC substrate in view of its versatility as shown in FIGS. 2 and 3. Specifically, the NPN output circuit 43 in the output driver 14 includes an NPN power transistor Q41 the output terminal of which is directly connected with a load device 45 whereas the PNP output circuit 44 includes an NPN transistor the output of which is connected with a load device 46 through a PNP power transistor Q42 externally attached to the IC substrate.
Incidentally, the output circuits 43 and 44 have known short-circuit protecting functions, respectively which are usually linked so that when one operates, the other also operates. A short-circuit protecting circuit suited for this function which requires no capacitor is suited for IC was proposed in JP-A-61-199416 to Tanigawa et al.
Since the NPN output circuit 43 is formed on the IC substrate 3, the output NPN power transistor Q41 is desired to be as small as possible, and so such an NPN power transistor as is not so large and can pass the driving current up to e.g. 100 mA is selected. In order to provide the driving current exceeding the 100 mA using such an NPN power transistor having a relatively small current capacity, the output therefrom is amplified by a transistor Q43 and a power transistor Q44 as shown in FIG. 3. Thus, the current permitted for the power transistor Q44 can be supplied to the load device 45. However, in the case of providing a large driving current in the above manner, the driving current flowing through the load device 45 flows in its most through the power transistor Q44 and almost does not flow through the NPN output circuit 43. Therefore, the short-circuit protection function of the NPN output circuit 43 does not work. In this case, in order to prevent the short-circuiting in the load device 45, a circuit having the short-circuit protection function externally attached to the IC substrate is separately used.
The display device 15 produces a lighting signal causing the display lamp 5 to flash on and off to indicate the detection state using the above output signal, or the operating state of the load device 2 using the driving signal.
The power supply circuit unit 9 transforms DC voltages between (Vcc and G) externally supplied through terminals 21 and 22 to supply the DC voltages required for the respective circuit units of the switch 1. The power supply circuit unit 9 is composed of a voltage regulating circuit 16 and a power supply resetting circuit 17. The voltage regulating circuit 16 serves to provide a stable DC voltage. The power supply resetting circuit 17 serves to monitor the output from the voltage regulating circuit 16 and to limit power supply until a stabilized voltage at a necessary level is obtained, thereby assuring a stabilized power supply. The power supply resetting circuit 17 recognizes the stability of the power supply to supply to the output driver 14 a signal permitting the driving signal to be output.
Meanwhile, in the case where the detection switch 1 is used for a two-wired AC circuit, a relatively large leakage current flows through the detection switch 1 when the load device 2 such as a relay is off so that as the case may be the load device 2 will not be completely turned off. In order to obviate such a phenomenon, the detection switch 1 is required to be operated by a small current. To this end, without using a power supply circuit unit 9 incorporated in the switch body, power may be supplied from an external constant voltage source for making a constant voltage on the basis of the AC power. For preparation of necessity of directly accepting an external DC power for driving the load device by the AC power like this case, terminals 27 and 28 for a jumper are provided on the IC substrate 3. The terminals 27 and 28 permit power to be supplied from the external power source when the power supply lines in the IC substrate are disconnected from the inner power supply circuit unit 9. Usually, terminals 27 and 28 are short-circuited by the jumper to use the power from the power supply circuit unit 9. On the other hand, in the case where power is to be supplied form the external power source, the jumper is removed to connect the terminal 27 with the external DC power source. In this case, the output driver 14 in the output circuit unit 8 is not used but the output from the integrating circuit 12 is used as a driving signal as it is.
Further, for the detection switch 1 to operate in low power consumption, the start-up speed of the switch 1 becomes low. The power supply resetting circuit 17 is not operable during the case, then a timer circuit is required to be separately attached to the above external constant power source in order to realize a long power supply resetting time.
The display lamp 5 which indicates the detection state or the operating state in response to the lighting signal is located at a position where it can be seen from the exterior of the detection switch 1. The display lamp 5 may be a light-emitting diode, a neon tube, an incandescent lamp, or the like.
The display manner of the display lamp 5, i.e. ON or OFF according to the detection signal, and indication according to the driving signal should be suitably selected in accordance with the purpose of using the detection switch 1 and the respective properties of the object to be detected and the load device. The display lamp which flashes on and off in accordance with the detecting signal is useful to monitor the presence of the object to be detected. The display lamp which flashes on and off in accordance with the driving signal is useful to monitor ON/OFF of the output circuit. For example, it is assumed that objects on a conveyer are classified using a photo-optical switch. In this case, in a system of detecting the object in terms of the light reflected from the object, as shown in FIG. 4, when the detector 4 receives the light reflected from the object, the detection circuit 7 generates a judgment signal and the output circuit unit 8 generates a driving signal based on the judgment signal. The detection signal and the driving signal are generated with the same timing so that the display lamp 5 displays both detection signal and driving signal. On the other hand, in a system of generating a detection signal when incident light is shaded by the object to be detected from the object, as shown in FIG. 5, the detection circuit 7 generates a judgment signal when the incident light on the detector 4 is shaded by the object to be detected, and the output circuit unit 8 generates a driving signal according to the judgment signal. The display lamp 5 displays either of the detection signal and the driving signal which are in an opposite phase to each other. Furthermore, in the case of using a sequencer with a low speed response time, as shown in FIG. 6, a suitable delay may inevitably be provided between the detection signal and the output signal.
The detection switch will be fabricated in accordance with individual purposes. If the type of the detection switch is one designed individually for a selected object to be monitored, a detection switch adaptive to monitor one object cannot be easily changed to one for another object. The detection switch has many applications under the various conditions of application and so must be changed in its design in accordance with the display manners as required.
The delay circuit 6 serves to delay the output signal from the detection switch 1 in order to cause the high speed response of the detector 4 to coincide with the low speed response in a drived device like a program controller, etc. The delay circuit 6 receives the judgment signal from the detection circuit unit 7 through a terminal 25 and sends a delayed judgment signal delayed within the circuit to the output circuit unit 8 through a terminal 26. Incidentally, if the terminal 25 and the terminal 26 are short-circuited by a jumper, the judgment signal relative to the object to be detected can be directly supplied to the output circuit unit 8. If the switch 1 is used with a driving device having a signal amplifying function, the output from the integrating circuit 12 can be directly used as a driving signal by connecting the terminal 25 with the driving device.
One concrete example of the delay circuit 6 is shown in FIG. 7. If the input side terminal 31 and output side terminal 32 in the delay circuit 6 in FIG. 7 are connected with the terminals 25 and 26 in FIG. 1, respectively, the detection switch 1 may have an off delay function. A resistor R1 and a capacitor C1 of the delay circuit (6) are used to set the off delay time. Resistors R3, R4 and R5 are used to provide a comparator 33 with hysteresis. Thus, chattering of the detection switch 1 can be prevented. Although the delay circuit 6 is incorporated within the detection switch 1, it is difficult to incorporate the delay circuit in the IC substrate 3 because the components such as capacitors required for the circuit arrangement are bulky. Also, it is not preferable to incorporate the delay circuit in the IC substrate for the convenience in design of setting different delay times. For these reasons, it is desired to attach the delay circuit outside the IC substrate 3.
Meanwhile, the detection switch described above is desired to be compact and inexpensive, and also the demand for supply of such a detection switch by mass-production is very great. However, the prior art requires components externally attached at various positions in order to assure the versatility in design so that the structure of the entire detection switch is made complicated and large scaled, therefore it was difficult to reduce the production cost.
In order to restrain the production cost, it is desired to integrate as many components as possible on an IC substrate. Therefore, it is preferable that a bulky component such as a reactance element is not used in the circuit and also no component is externally provided. However, the detection switch satisfying such conditions lost its essential switch function, or was burdened with many detection conditions. As a result, in many cases, the product value of the detection switch was lost.